This gallery has a 28mm hole in the center which you can simply add a BC lampholder to it clamping the lampholder in place with its shade rings.
Has 6 Decorative holes in the top for heat ventilation.
And has 3 screws to hold the shade in place, these can be done up with a slotted screw driver if needed.
Center hole size: 28mm
Shade Hole Diameter: 3 1/4" (82.55mm)
Material: Brass, Old English plated